The present invention generally relates to inductive power transfer devices for charging or powering cordless appliances.
Currently, cordless electrically operated devices are charged by a source of electrical energy only when the device and source are connected to one another. Normally, the source includes some sort of pedestal to which the device is connected before charging may occur. The drawbacks of such an arrangement are self-evident. For example, when working with a cordless drill, it is often necessary to mount a battery which must be removed from the drill, or the drill itself, on the charger before the charging process can begin. If the charger is not kept in close proximity, the drill battery must be moved to the charger. The present invention differs significantly from the known prior art wherein the source and devices are specifically matched to only operate when the receiver is mounted on the holder for recharging. The present invention provides a novel system for automatically charging a device whenever it is placed on a rest surface without a direct electrical connection, regardless of the orientation of the device on the surface.
Accordingly, it is a primary object of the invention to provide an induction power transfer device for an appliance including a housing and a plurality of primary inductors or coils arranged in an array within the housing. A circuit connects the inductors with a power supply and a plurality of switches connect each inductor with the circuit. The switches are operable to selectively activate respective primary inductors so that when an appliance having at least one secondary inductor is placed on the housing, power is transferred to the appliance via a transformer defined by the primary inductors and the secondary inductor.
According to a further embodiment of the invention, at least one of the primary inductors has a longitudinal axis arranged normal to the axes of the other primary inductors.
The housing preferably has a flat top wall beneath which the primary inductors are arranged in a plane parallel to the wall. An appliance placed on the wall has its secondary inductor inductively coupled with at least one of the primary inductors.
According to a further object of the invention either the inductive transformer device or the appliance may include an alignment mechanism to assist in aligning their respective inductors to maximize power transfer.
According to another object of the invention, capacitors are provided for each primary inductor to balance the inductance thereof.
In accordance with the invention, a user could merely place the appliance such as a cordless power tool, laptop computer, or recording device on a table, shelf or other common storage member and the charging process occurs automatically, regardless of the orientation of the receiver relative to the charging source. This would result in the appliance being charged whenever it is not in use, rather then merely resting on a work table between uses as in current practice.
The unique assembly of the present invention assures that the transfer of inductive power will occur regardless of the orientation of the appliance relative to the charging source. To achieve this result, the source may be configured with a number of coils that are arranged in predetermined positions that optimize the transfer of power to the appliance for certain applications such as a maximum duty cycle, i.e., power transfer density, or minimum obtrusiveness.